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Early this morning, the Asia Pacific Network Information Centre (APNIC) announced that it had been allocated two /8 address blocks from the Internet Assigned Numbers Authority (IANA
). Those two blocks, 39/8 and 106/8, were the last unallocated blocks in the IANA free pool of IPv4 address available to Regional Internet Registries (RIR). With the allocation, the final days of IPv4 have moved closer as the number of available addresses that can be allocated will dwindle.

"Please be aware, this will be the final allocation made by IANA under the current framework and will trigger the final distribution of five /8 blocks, one to each RIR under the agreed global policy for the allocation of the remaining IPv4 address space, APNIC wrote on its website.

While the IANA free pool is now gone, that doesn't mean that IPv4 address space itself has been exhausted. The RIRs make requests from IANA for free, unallocated space which is then allocated by the RIRs to carriers and businesses. Each /8 allocation includes approximately 16 million addresses. In total, there could be 4.3 billion IPv4 addresses in use, were they all fully allocated.

APNIC expects to continue to make normal allocations of IPv4 address space to its constituents for the next three to six months. After that, it will grant only smaller blocks of address space that could extend the allocation another five years.

In the U.S., the American Registry for Internet Numbers (ARIN) is the RIR responsible for address allocation. John Curran, CEO of ARIN, told InternetNews.com that as of January 1, 2011 (the date of the last number resource report), ARIN had the equivalent of 4.92 /8 blocks. Curran was not able to specify when ARIN will actually run out of IPv4 address space to allocate.

"We have no official forecast, and any estimate would change rapidly depending on requests received," Curran said. "Based on solely historical tendencies, 6 to 9 months from final IANA allocation till ARIN exhaustion would not be an unreasonable expectation."

More impetus for the IPv6 migration

With freely available, unallocated IPv4 addresses almost gone, the move to the next generation IPv6 addressing system which provides significantly more address space than IPv4 must begin in earnest. IPv6 has a 128 bit addressing system that can provide 340 trillion trillion trillion (34 x 10 to the 38th power) Internet addresses.

To date, IPv6 adoption has been slow, though the RIRs have been advocating for its adoption.

"The RIRs have been working with network operators at the local, regional, and global level for more than a decade to offer training and advice on IPv6 adoption and ensure that everyone is prepared for the exhaustion of IPv4," Axel Pawlik, managing director of RIPE (Réseaux IP Européens), the RIR for Europe told InternetNews.com. "Post IPv4 depletion, RIPE will continue to distribute Internet number resources, including IPv6 addresses."

Pawlik added that the transition to IPv6 from IPv4 represents an opportunity for even more innovative applications without the fear of running out of essential Internet IP addresses.

Though IPv4 is now nearly exhausted, the move to IPv4 will take time. The Internet Society has scheduled World IPv6 day for June to test the addressing system on major websites including Google and Facebook, but there is still work to be done. The immediate future is not a move away from IPv4, but rather a move to include IPv6.

"Internet users need to realize that the Internet will be in transition over several years, with both IPv4 and IPv6 running in parallel," ARIN's Curran said. "Organizations need to IPv6 enable their Web site, so that both existing IPv4 and new IPv6-connected Internet users can directly access it."